Boundary shape function unifies families of stopping
rules
Wang
& Tsiatis (1987) based families
OBrien
& Fleming (1979); Pocock (1977)
Also used by Emerson & Fleming (1989); Pampallona
& Tsiatis (1994)
Triangular
test (Whitehead, 1983)
Seq
cond probability ratio test (Xiong & Tan, 1994)
Conditional
or predictive power
Peto-Haybittle
(using Burington & Emerson, 2003)